A lot of things on TPB are not up for sale in the first place. It's much like YouTube a tiny slice of content is vary popular and much of that is pirated, but for every "Battle at Kruger" http://www.youtube.com/watch?v=LU8DDYz68kM theres a lot of Let's Play Unreal World 10(1/2) Buy a Boat http://www.youtube.com/watch?v=0JOeQJGDgNw.

As to TPB specificly it's think anime fan subs for nitch shows that are never going to be released in the US.